1) Field of the Invention
The present invention relates to an image forming apparatus using an electrographic method, such as a copier, a printer, a facsimile, or a multifunction product thereof, which forms an image of multiple colors, such as a color image, a process cartridge and a developing unit installed therein, and an image forming method.
2) Description of the Related Art
Conventionally, in a color image forming apparatus such as a color copier, process cartridges (or developing unit) corresponding to toners of multiple colors (yellow, magenta, cyan, and black) are detachably installed in an image forming apparatus main unit. These process cartridges (or developing unit) are appropriately replaced by a new one, as the process cartridge mechanically wears out.
Specifically, in a developing unit in a new process cartridge, for example, (1) a two-component developer including a carrier and a toner of any one color of yellow, magenta, cyan, and black, or (2) a one-component developer including a toner of any one color of yellow, magenta, cyan, and black is stored beforehand in a space completely isolated by a sealing member.
After the sealing member in the developing unit in the new process cartridge is taken away, four process cartridges are respectively installed in the respective installation sections in the image forming apparatus main unit. Thereafter, when a photosensitive drum (an image carrier) in the process cartridge deteriorates, or the one-component developer in the cartridge has been consumed, to reach the end of the service life, with the operation of the image forming apparatus, the existing process cartridge installed in the image forming apparatus main unit is taken out by an operator such as a user or a maintenance person. A new process cartridge is then installed newly in the apparatus main unit.
In the image forming apparatus in which the process cartridges (or developing unit) are detachably installed, it is necessary that the respective process cartridges are installed precisely in the corresponding installation section. That is, an installation error such that a process cartridge of a certain color is installed in an installation section of a different color should not be made by the operator.
For this purpose, in the image forming apparatus, such a technique is mainly used that a shape difference is provided in the four process cartridges and the installation sections in the apparatus main unit respectively corresponding to the four process cartridges, to ensure the incompatibility (For example, see Japanese Patent Application Laid-open No. 2003-84534).
The sealing member installed in the developing unit in the process cartridge is for preventing the toner stored in the developing unit from scattering from the process cartridge (For example, see Japanese Patent Application Laid-open No. H11-231759).